This invention relates generally to joints for ductile iron pressure pipe and more particularly to a tool for disconnecting ductile iron pipes which have been joined with toothed gaskets.
In many applications where pipes are joined in telescoping relationship, for example water and sewer pipes, the smooth or spigot end of one pipe is inserted into the socket end of the engaging pipe. The socket end has an opening large enough to receive the spigot end of the enclosed pipe. A gasket is inserted in the socket end of the enclosing pipe and prevents leakage of fluid from the joint by forming a seal between the two pipes. In applications where the fluid such as water for fire mains or municipal water distribution is under high pressure, various means are used to prevent separation of the two pipes. Although pipes may be connected with bolted flanges, blocks or other external restraining devices to prevent separation, these methods are costly and time consuming.
Another known method to prevent separation of the pipes is to use a rubber gasket which serves as a fluid seal and which also has toothed metal segments spaced uniformly around its inner perimeter. The metal segments pivot about a bead to allow the spigot end of one pipe to be inserted into the socket end of the other pipe while preventing withdrawal of the inserted pipe under high fluid pressure conditions. The toothed metal segments bite into the outer surface of the spigot of the inserted pipe and prevent withdrawal of the inserted pipe. Such gaskets are described in U.S. Pat. No. 5,295,697 assigned to U.S Pipe & Foundry Company, Birmingham, Ala., USA 35222, and available under the name FIELD LOK from the same company.
The significant holding power of this type of gasket represents a drawback when a pipe joint must be taken apart. In order to disconnect pipes joined with one of these gaskets, it is first necessary to release all of the individual toothed metal segments. If a single one of the segments is not released, it will be impossible to separate the pipes, even with heavy construction equipment. In the prior art, the pipes have been separated using an array of narrow shim-type tools which are driven into the pipe joint to release each individual segment. However, such tools are prone to breakage and are tedious to use because the exact location of each toothed segment around the periphery of the pipe joint is not known. If all of the teeth cannot be released, the pipes must then be separated by cutting. This requires subsequent patching or replacement with new pipes, which is wasteful and time consuming.